We have analysed high‐dispersion echelle spectra (R ≳ 50 000) of red giant members for four open clusters to derive abundances for many elements. The spread in temperatures and gravities being very small among the red giants nearly the same stellar lines were employed thereby reducing the random errors. The errors of average abundance for the cluster were generally in the range 0.02–0.07 dex. Our present sample covers Galactocentric distances of 8.3–10.5 kpc. The [Fe/H] values are −0.02 ± 0.05 for NGC 752, −0.07 ± 0.06 for NGC 2360, −0.11 ± 0.05 for NGC 1817 and −0.19 ± 0.06 for NGC 2506. Abundances relative to Fe for elements from Na to Eu are equal within measurement uncertainties to published abundances for thin‐disc giants in the field. This supports the view that field stars come from disrupted open clusters.

We have collected high-dispersion echelle spectra of red giant members in the twelve open clusters (OCs) and derived stellar parameters and chemical abundances for 26 species by either line equivalent widths or synthetic spectrum analyses. We confirm the lack of an age−metallicity relation for OCs but argue that such a lack of trend for OCs arise from the limited coverage in metallicity compared to that of field stars which span a wide range in metallicity and age. We confirm that the radial metallicity gradient of OCs is steeper (flatter) for R gc < 12 kpc (>12 kpc). We demonstrate that the sample of clusters constituting a steep radial metallicity gradient of slope −0.052±0.011 dex kpc −1 at R gc < 12 kpc are younger than 1.5 Gyr and located close to the Galactic midplane (| z| < 0.5 kpc) with kinematics typical of the thin disc. Whereas the clusters describing a shallow slope of −0.015±0.007 dex kpc −1 at R gc > 12 kpc are relatively old, thick disc members with a striking spread in age and height above the midplane (0.5 < | z| < 2.5 kpc). Our investigation reveals that the OCs and field stars yield consistent radial metallicity gradients if the comparison is limited to samples drawn from the similar vertical heights. We argue via the computation of Galactic orbits that all the outer disc clusters were actually born inward of 12 kpc but the orbital eccentricity has taken them to present locations very far from their birthplaces.

We have analyzed high-resolution echelle spectra of red giant members for seven open clusters in the Galactic anticentre direction to explore their chemical compositions. Cluster membership has been confirmed by radial velocity. The spread in temperatures and gravities being very small among the red giants, nearly the same stellar lines were employed for all stars thereby reducing the abundance errors: the errors of the average abundance for a cluster were generally in the 0.02 to 0.05 dex range. Our present sample covers Galactocentric distances of 8.3 to 11.3 kpc and an age range of 0.2 to 4.3 Gyr. A careful comparison of our results for the cluster NGC 2682 (M 67) to other high-resolution abundance studies in the literature shows general good agreement for almost all elements in common.

We have analyzed high-resolution echelle spectra of red giant members for seven open clusters in the Galactic anticentre direction to explore their chemical compositions. Cluster membership has been confirmed by radial velocity. The spread in temperatures and gravities being very small among the red giants, nearly the same stellar lines were employed for all stars thereby reducing the abundance errors: the errors of the average abundance for a cluster were generally in the 0.02 to 0.05 dex range. Our present sample covers Galactocentric distances of 8.3 to 11.3 kpc and an age range of 0.2 to 4.3 Gyr. A careful comparison of our results for the cluster NGC 2682 (M 67) to other high-resolution abundance studies in the literature shows general good agreement for almost all elements in common.

Several abundance analyses of Galactic open clusters (OCs) have shown a tendency for Ba but not for other heavy elements (La−Sm) to increase sharply with decreasing age such that Ba was claimed to reach [Ba/Fe] ≃ +0.6 in the youngest clusters (ages < 100 Myr) rising from [Ba/Fe]= 0.00 dex in solar-age clusters. Within the formulation of the s-process, the difficulty to replicate higher Ba abundance and normal La−Sm abundances in young clusters is known as the barium puzzle. Here, we investigate the barium puzzle using extremely highresolution and high signal-to-noise spectra of 24 solar twins and measured the heavy elements Ba, La, Ce, Nd and Sm with a precision of 0.03 dex. We demonstrate that the enhanced Ba II relative to La−Sm seen among solar twins, stellar associations and OCs at young ages (<100 Myr) is unrelated to aspects of stellar nucleosynthesis but has resulted from overestimation of Ba by standard methods of LTE abundance analysis in which the microturbulence derived from the Fe lines formed deep in the photosphere is insufficient to represent the true line broadening imposed on Ba II lines by the upper photospheric layers from where the Ba II lines emerge. As the young stars have relatively active photospheres, Ba overabundances most likely result from the adoption of too low a value of microturbulence in the spectum synthesis of the strong Ba II lines but the change of microturbulence in the upper photosphere has only a minor affect on La−Sm abundances measured from the weak lines.

We have observed high-dispersion echelle spectra of main-sequence stars in five nearby young associations -Argus, Carina-Near, Hercules-Lyra, Orion and Subgroup B4 -and derived abundances for elements ranging from Na to Eu. These are the first chemical abundance measurements for two of the five associations, while the remaining three associations are analysed more extensively in our study. Our results support the presence of chemical homogeneity among association members with a typical starto-star abundance scatter of about 0.06 dex or less over many elements. The five associations show log ǫ(Li) consistent with their age and share a solar chemical composition for all elements with the exception of Ba. We find that all the heavy elements (Y, Zr, La, Ce, Nd, Sm and Eu) exhibit solar ratios, i.e., [X/Fe] ≃ 0, while Ba is overabundant by about 0.2−0.3 dex. The origin of the overabundance of Ba is a puzzle. Within the formulation of the s-process, it is difficult to create a higher Ba abundance without a similar increase in the s-process contributions to other heavy elements (LaSm). Given that Ba is represented by strong lines of Ba ii and La-Sm are represented by rather weak ionized lines, the suggestion, as previously made by other studies, is that the Ba abundance may be systematically overestimated by standard methods of abundance analysis perhaps because the upper reaches of the stellar atmospheres are poorly represented by standard model atmospheres. A novel attempt to analyse the Ba i line at 5535Å gives a solar Ba abundance for stars with effective temperatures hotter than about 5800 K but increasingly subsolar Ba abundances for cooler stars with apparent Ba deficiencies of 0.5 dex at 5100 K. This trend with temperature may signal a serious non-LTE effect on the Ba i line.

We have analysed high-dispersion echelle spectra (R = 60000) of red giant members of five open clusters to derive abundances for many elements from Na to Eu. The [Fe/H] values are −0.06 ± 0.03 for Stock 2, −0.11 ± 0.03 for NGC 2168, −0.01 ± 0.03 for NGC 6475, 0.00 ± 0.03 for NGC 6991 and −0.07 ± 0.03 for NGC 7662. Sodium is enriched in the giants relative to the abundance expected of main sequence stars of the same metallicity. This enrichment of [Na/Fe] by about +0.25 attributed to the first dredge-up is discussed in the light of theoretical predictions and recently published abundance determinations. Abundance ratios [El/Fe] for other elements are with very few exceptions equal to those of field giants and dwarfs, i.e., [El/Fe] ≃ 0.00 for [Fe/H] ∼ 0.0. An exception is the overabundance of La, Ce, Nd and Sm in NGC 6991 but this is consistent with our previous demonstration that the abundances of these s-process products vary by about ±0.2 among clusters of the same [Fe/H], a variation found also among field giants and dwarfs.

We have detected CH + and CH molecular absorption lines from the youngcompact planetary nebula IC 4997 from high resolution optical spectra. A high-resolution infra-red (H and K bands) spectrum provides detection of H 2 emission lines among many other lines. The H 2 lines provide an excitation temperature of 2100 K which may result from UV fluorescence in the envelope or from shocks formed at the interface between an expanding outflow of ionized gas and the neutral envelope ejected when the star was on the AGB. It is suggested that the CH + may result from the endothermic reaction C+H 2 →CH + +H. Intriguingly, CH + and also CH show a higher expansion velocity than H 2 emission suggesting they may be part of the post-shocked gas.